Brain volume
The size of the brain is a frequent topic of study within the fields of anatomy and evolution. Brain size can be measured by weight or by volume (via MRI scans or by skull volume). The relationship between brain size and intelligence is frequently a topic of research.
Studies on human brain size, largely based on participants of European ancestry, tend to find an average adult brain volume of 1260 cubic centimeters (cm3) for men and 1130 cm3 for women. There is, however, substantial variation between individuals; one study of 46 adults, aged 22–49 years and of mainly European descent, found an average brain volume of 1273.6 cm3 for men, with a range of 1052.9 to 1498.5 cm3, and 1131.1 cm3 for women, with a range of 974.9 to 1398.1 cm3.
The right cerebral hemisphere is typically larger than the left, whereas the cerebellar hemispheres are typically closer in size. The adult human brain weighs on average about 1.5 kg (3.3 lb). The average weight is about 1370 g in men and about 1200 g in women.
Brain size has increased considerably over the course of humans' recent evolutionary history. Homo erectus, a relative of humans, had a brain size of 1,100 cm3. Homo floresiensis, with a brain size of 380 cm3.Neanderthals had a slightly larger brain than modern humans, perhaps due to larger visual systems.
Some studies suggest that the average brain size has been decreasing over the past 28,000 years. Others suggest that the cranial capacity for males is unchanged, but that the cranial capacity of females has increased.
A number of studies have found correlation between variation in brain size in cranial capacity and geographic ancestry in humans. This variation in cranial capacity is believed to be primarily caused by climatic adaptation that favor large round heads in colder climates because they conserve heat and slender heads in warm climates closer to the equator (See Bergmann's rule and Allen's rule).
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